This invention is related to ceramic window materials and, more particularly, to densified ternary sulfides to be used as infrared window materials and fabrication thereof.
Infrared transmitting materials particularly for the 8-14 .mu.m region (1 .mu.m is equal to 10.sup.-6 meters) are necessary for sensor windows and domes on satellites, missiles and other similar devices. These materials must be chemically stable, abrasion resistant, have low coefficients of thermal expansion, high melting temperatures and good optical transmission characteristics in the desired region of the infrared. The materials used in the past are alkali halides, zinc sulfide and zinc selenide. However, these materials do not have the hardness and abrasion resistance required for most of the above-enumerated applications. Furthermore, the optical transmission of the zinc sulfide and zinc selenide materials is deficient at the long wavelength end of the infrared region of interest. It is also desirable that any window material must be a theoretically dense compact of high purity in order to fulfill the criteria listed above. Single crystals are considered ideal for subject applications, but it is extremely difficult to prepare single crystals in the sizes required for window applications. Polycrystalline ceramics are suitable as windows, provided that densification is complete, scattering centers are kept to a sufficiently low level, and the ceramics are made from cubic compounds to avoid optical anisotropy from the randomly oriented grains. It is thus desirable to have some infrared transmitting materials having the above-mentioned characteristics.